Functional testing is an integral part of aircraft manufacturing and maintenance processes which ensures that the aircraft systems operate properly so that an aircraft can be flown safely. Functional testing of modern commercial and military aircraft is performed on most, if not all of the components in each aircraft system. During functional testing, components are tested separately and/or as an integral part of a subsystem to ensure that the components and the subsystems will function as intended. Proper testing of individual components and subsystems often requires that each component or subsystem be tested in different modes for response to different external conditions. For example, thorough testing of an aircraft flight control subsystem may require testing of the subsystem in conditions that simulate fully and partially operative, and inoperative states of a hydraulic system that moves the flight control surfaces. Thus, aircraft subsystem functional testing often requires a large number of tests that are redundant except for variations in conditions external to the tested component or the subsystem. Accordingly, aircraft functional testing demands the running of a large number of test procedures, many of which include a large number of test steps.
The number, complexity, and exactness of the required test procedures have made aircraft functional testing a difficult, time-consuming activity. Moreover, when an aircraft is being assembled, efficiency often demands that each component or subsystem be tested soon after the component or subsystem is installed in the aircraft. Immediate testing makes it possible to repair or replace a malfunctioning component before later assembly complicates access to the component. Often though, components that provide stimulus to a newly installed component to be tested, or that respond to output signals therefrom, are not operative or even installed in the aircraft when it is desirable to test the newly installed component. The inoperativeness of the complementary components makes testing of newly installed components a difficult, if not impossible, task.
Other difficulties are associated with the level of support required to perform the necessary testing procedures. Technicians must know the different tests that need to be performed on each aircraft component and how to operate the complicated equipment needed to perform the tests. Whenever the testing procedures for an aircraft, or a particular component thereof, change, the technicians are required to learn the new testing procedures. Moreover, given the number of test procedures that need to be performed, and the slight variation between some of the procedures, there is a distinct possibility that even the most conscientious technician may improperly perform a given test. Improper testing of an aircraft component that may affect the safe operation of the aircraft should clearly not occur.
The scheduling of functional tests that need to be performed during the aircraft manufacture and maintenance processes adds to the complexity of these processes. In many aircraft manufacturing environments, personnel who assemble aircraft are not the personnel who do the testing. Consequently, test personnel must rely on written records completed by the assemblers to know when components and subsystems have been installed in the aircraft so that they can be tested. In aircraft maintenance environments, some functional tests need to be performed each time a component is repaired or replaced, other tests need to be performed periodically based on the number of hours the aircraft has been in flight, while still other functional tests must be periodically performed based on how many segments the aircraft has flown (i.e., the number of takeoffs and landings the aircraft has made). Maintenance personnel performing the tests need to review numerous records to determine what tests need to be performed on an aircraft. All this review of records during the aircraft manufacture and maintenance processes adds to the time required to perform the tests. Moreover, the scheduling process requires that manufacturing and maintenance personnel make records that accurately reflect work done on an aircraft, and that test personnel thoroughly review the records and, upon the basis of the review, correctly determine the functional tests that need to be performed on the aircraft.
Aircraft functional testing also requires that component test records be maintained for review by regulatory agencies. Test records are generated and maintained so that the agencies can verify that the components have been tested to ensure that they operate properly. Maintenance personnel also find access to component test result histories helpful. Test records may, for example, show that different types of navigation computers installed in a particular aircraft frequently fail a certain test. Maintenance personnel reviewing the test records for the navigation computers can then use the information therein as a basis upon which to conclude that the faults may not be with the computers, but with one or more of the components connected to them. Accordingly, it is desirable, if not mandatory, to keep a record of the manufacturing and post-manufacturing maintenance functional tests run on an aircraft.
The record keeping that is required for each functional test adds to the complexities of the aircraft testing process. Proper record keeping requires that the result of each test be recorded as soon as the results are known. This step increases the overall time it takes to perform each test. Paper record keeping of test results requires large numbers of records, in the form of test report sheets, to accompany an aircraft as it is subjected to manufacturing and maintenance testing. Filing and maintaining test report sheets and any reduction of data thereof are time-consuming tasks that add to the overall cost of the testing. Furthermore, proper record keeping requires that the results of each test procedure be accurately recorded, and that other transcribing the original record make true copies of same. Each of these steps involve human activity, which means that there is the possibility that human error will result in inaccurate test record results being created and maintained.
Stand-alone test devices have been developed for the automated testing of some aircraft components and subsystems. These test devices typically are connected to specific ports on the aircraft associated with the particular component or subsystem the device is designed to test. Such test devices, however, do not facilitate the process of performing the large number of different test procedures that are now required to certify that an aircraft is airworthy.